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Researchers compared two groups of 11-year-old children, and found that the group that had been breast-fed for a longer average time was no more likely to be obese that the group breast-fed for a shorter time.

Previously reported results from the trial showed that breast-feeding did not lower a child's risk of being overweight or obese at age 6.

"Nevertheless, breast-feeding has many health advantages" for children, including lower risk of gastrointestinal infections and eczema in infancy, and improved cognitive development at age 6, the researchers wrote in their study. Several of the study authors have previously received money from Nestle, which sells infant formula.

The trial was designed to look at the effects of a program aimed at promoting exclusive breast-feeding (without the addition of infant formula to the baby's diet) [s1] for a longer time. In the new study, researchers led by Richard Martin, a professor of epidemiology at the University of Bristol in England, randomized 17,000 breast-feeding mothers in Belarus to either enter the program, which included additional help from health-care workers in getting started with breast-feeding and continuing lactation support, or to receive the typical amount of support given to mothers.

Indeed, 43 percent of the mothers in the program were exclusively breast-feeding their infants at 3 months of age, whereas 6.4 percent of mothers in the control group were doing so. Babies in the intervention group were also more likely to be exclusively breast-fed at 6 months, and breast-fed to any degree at a year.

The new findings show that when the children were 11 years old, there were no differences between the control and intervention groups in terms of the children's body mass indexes, amount of body fat, waist size or likelihood of being obese.

Although previous research has suggested that breastfeeding for a longer time may lower a child's risk of obesity, these studies were observational, and had confounding variables that could have accounted for the differences between the groups.

The researchers noted that all mothers in the study initiated breastfeeding with their infants, so their findings may not apply to a comparison of infants who are breast-fed to those who are formula-fed from the outset.

The study was very well designed and conducted, said Dr. Ruth Lawrence, professor of gynecology and pediatrics at the University of Rochester Medical Center in New York.

The study investigators will likely be criticized because of the funding they have received, she said. "Formula companies are known to be aggressive."

But the trial in this study is known by those in the field to be well designed and orchestrated, Lawrence said.

The biggest problem with the study is the lack of a comparison group of babies that were fed infant formula exclusively. Such formula feeding is known to be linked with a higher risk of obesity, she said.

The results are detailed March 12 in the Journal of the American Medical Association.